1. Field of the Invention
The present invention relates to an ophthalmic apparatus, a control method for the apparatus, and a storage medium and, more particularly, to an ophthalmic apparatus which has an adaptive optical function of measuring and correcting the aberration of an eye to be examined and can correct the aberration in accordance with imaging states, a control method for the apparatus, and a storage medium.
2. Description of the Related Art
Recently, as an ophthalmic imaging apparatus, an SLO (Scanning Laser Ophthalmoscope) apparatus like the one disclosed in U.S. Pat. No. 4,213,678 has been widely used, which two-dimensionally irradiates the fundus with a laser beam and receives the reflected light.
In addition, an imaging apparatus using low-coherence light interference has been put into practice. This apparatus is called OCT (Optical Coherence Tomography), which is used in the field of ophthalmology, in particular, to obtain a tomogram of the fundus or its neighboring region. As a type of OCT, there is available a method called TD-OCT (Time Domain OCT) disclosed in U.S. Pat. No. 5,321,501 or Japanese Patent Laid-Open No. 2002-515593. As another type of OCT, a method called SD-OCT (Spectral Domain OCT) is disclosed in Handbook of Optical Coherence Tomography (2006) (pp. 145, 149, FIGS. 2, 3; p. 338, FIG. 1).
Such an ophthalmic imaging apparatus has recently been improved in resolution by, for example, increasing the NA of a laser irradiation optical system. When, however, imaging the fundus, it is necessary to perform imaging through the optical tissue of the eye, such as the cornea and crystalline lens. With an increase in resolution, the aberration of the cornea and crystalline lens has greatly influenced the image quality of captured images. Under the circumstances, studies have been conducted on AO (Adaptive Optics)-SLO and AO-OCT incorporating, in an optical system, AO which measures and corrects the aberration of the eye. AO-OCT is disclosed in, for example, Y. Zhang et al., Optics Express, Vol. 14, No. 10, 15 May 2006. AO-SLO and AO-OCT generally measure the wavefront of the eye by the Shack-Hartmann wavefront sensor system. The Shack-Hartmann wavefront sensor system is a technique of measuring the wavefront of the eye by irradiating the eye with measurement light and making a CCD camera receive the reflected light through a microlens array. It is possible to perform high-resolution imaging by driving wavefront correction devices such as a deformable mirror and a spatial phase modulator so as to correct a measured wavefront, and imaging the fundus through the devices.
A fundus imaging apparatus including the above conventional adaptive optical system is generally configured to keep a light-receiving unit for reflected light and a wavefront sensor in an optically conjugate relation so as to allow the wavefront sensor to measure aberration similar to the aberration state at the light-receiving unit. In many cases, such apparatuses perform feedback control, that is, repeatedly driving the wavefront correction devices based on the information measured by the wavefront sensor. The reason for feedback control is to cope with errors between instruction values and actual correction amounts and variations in aberration depending on the states of the tear fluid and refractive adjustment of the eye.
In this arrangement, it should be able to reduce the aberration of signal light at the light-receiving unit and improve the light reception efficiency by reducing the aberration using the wavefront sensor. Even if, however, the aberration measured by the wavefront sensor becomes minimum, the light reception efficiency may not become maximum depending on the influences of measurement errors in the wavefront sensor due to the influence of stray light, aberration existing in the optical system of the light-receiving unit such as a collimator, and disturbance in the conjugate relation between the wavefront sensor and the light-receiving unit.
It may be possible to cope with disturbance in the conjugate relation between the wavefront sensor and the light-receiving unit and aberration in the light-receiving unit by performing detection, adjustment, and the like at the time of assembly of the apparatus. However, it is very difficult to cope with the influence of stray light to the wavefront sensor because it is difficult to predict it in advance. Even if it is possible to cope with this, it is necessary to change aberration correction control depending on individual differences among apparatuses and installation conditions. This imposes a very heavy load in terms of apparatus adjustment.
In consideration of the above problems, the present invention provides a technique which allows the performance of aberration correction in accordance with imaging states and the performance of imaging with high image quality.